Bullets



June 1962 w, A. ZISMAN ETAL 3,040,652

BULLETS Filed Nov. 19, 1959 2 LEAD lNTERED POLYMER WASHER INVENTOR5WILLIAM A. ZISMAN VINCENT e. FITZSIMMONS ATTORNEY United States PatentBULLETS William A. Zisman, Silver Spring, Md., and Vincent G. FitzSimmons, McLean, Va., assignors to the United States of America asrepresented by the Secretary of the Navy Filed Nov. 19, 1959, Ser. No.854,209

2 Claims. (Cl. 102-93) (Granted under Title 35, US. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to ammunition, more particularly to animprovement in projectiles of low melting point metal which is designedto increase the firing life of gun barrels.

This application is a continuation-in-part of our application, SerialNo. 480,624, filed January 7, 1955 now US. Patent No. 2,928,348.

Metal fouling, if unchecked, will eventually terminate the firing lifeof gun barrels. It is caused by the deposition of softer metal from theprojectiles on to the rifiing of the gun during firing and byaccumulation produces a roughened surface on the rifiing which isreflected in deviations in the spin imparted to the projectile andthere'- by loss in accuracy in the gun fire. Loss in muzzle velocity ofthe projectile may also result from metal fouling.

We have found that the firing life of gun barrels can be materiallyincreased by so modifying the projectile of low melting point metal thatthe portion of its surface which normally makes contact with the rifiingof the gun on firing is in part essentially sinteredpolytetrafluoroethylene. Polytetrafluoroethylene is a polymer known inthe trade as Teflon. By so modifying the projectile, there eventuates,on firing of the gun, a system of contact between the projectile and therifiing which is not metalto-metal but polymer-to-polymer. This flowsfrom the fact that sintered polymer is transferred from the projectileto the rifiing by rubbing to form on the latter a thin coating or filmof the sintered polymer. The coating on the rifiing does not build up byaccumulation to an undesirable degree of thickness due to thenon-self-adhering property of the sintered polymer, the thickness of thecoating being that of the thin film as initially applied by the transferfrom the projectile. When breaks occur in the film, renewal of the openportions is effected in the same manner; the exposed metal portions ofthe rifiing receiving sintered polymer by transfer from the subsequentlyfired projectile. A reverse arrangement in which the rifiing is coatedwith sintered polymer and the projectiles are of the usual constructionis impractical since movement of the projectile over the rifiing willremove portions of the coating until eventually it is worn oif.

Among the beneficial results flowing from the presence of the sinteredpolymer on or as that portion of the surface of the projectile whichcontacts the rifiing of the gun, is the absence of metal fouling.Another beneficial result is reduction in the rate of wear of the gunbarrel by friction, the sintered polymer having a low coefficient offriction. A further beneficial result and one of importance to rapidfire guns, especially those which are automatic, is reduction in theoccurrence of heat erosion of the gun barrel. The sintered polymer has alow thermal conductivity and this property in the polymer film on therifiing serves to delay transfer of heat from the hot, high temperaturegases to the metal of the surface of the gun bore and by consequence,promotes discharge of a greater portion of the heat from the gun barrelby "ice Another beneficial result is a greater from firing debris in thegun barrel, the sintered polymer surface on the projectile having theremarkable property of cleaning the gun barrel. Still another beneficialresult is a tendency to give a greater muzzle velocity for theprojectile. Yet another beneficial result is elimination of the need ofoiling the projectile with consequent avoidance of pick-up of dust andsand by the oil.

Projectiles of low melting point metal, e.g., a lead bullet, aremodified in accordance with the invention by making a preformed insertof essentially sintered polytetrafluoroethylene an integral part of theprojectile. The insert in the form of a ring or washer is inset in theperiphery of the projectile to form part of the surface which normallycontacts the rifiing of the gun and with the low melting point metalforms a unitary, one-piece structure.

Modification of the projectiles in accordance with the invention isillustrated in the single figure of the accompanying drawing which formspart of the description of the invention.

In the drawing:

The single FIGURE shows a small arms projectile of low melting pointmetal modified in accordance with the invention through the inclusion ofan insert of sintered polytetrafluoroethylene, the periphery of whichforms part of the surface of the projectile.

Referring to the single figure of the drawing, the projectile l of lowmelting point metal is a lead bullet which contains as an integral partthereof, a washer 2 of sintered polytetrafluoroethylene. A coating ofthe sintered polymer cannot be successfully applied to low melting pointmetals because of the high temperature necessary for sintering of thepolymer. The washer 2 is located in the bullet behind the ogive and isconterminous with the adjacent or bearing surface of the bullet. Asuitable thickness of the sintered polymer washer 2 is on the order of.025 inch for all small arms bullets, regardless of caliber. Asillustrated, the composite bullet of the invention is for a .30 caliberrifle.

The new composite bullets may be made by casting in bullet molds in theusual way with the modification that the washer 2 of the sinteredpolymer is previously placed in the predetermined position in the moldcavity. The hole in the washer 2 of sintered polymer should be largeenough to allow the molten, low melting point metal, such as lead or oneof the usual lead alloys, to flow through and fill the bottom as well asthe upper portion of the bullet mold cavity, whereby on cooling thecasting embraces the washer of sintered polymer as an integral part ofthe bullet. The washer 2 can be formed by cutting from a tape of thesintered polymer of the required thickness, the outer diameter of thewasher being that of the bullet. The washer is dropped into the moldcavity to lie in a horizontal position and is located at the properlevel by virtue of the convergence of the walls of the mold cavity whichare tapered to form the ogive of the bullet.

Instead of the use of convergence of the walls of the mold cavity todetermine the position of the washer of sintered polymer in the bullet,one may employ a Washer of a diameter which is but very slightly greaterthan the inside diameter of the mold cavity and push this slightlyoversize diameter washer into the section of the mold cavity whichdefines the bearing portion of the bullet to the desired depth, wherebyselected positioning of the sintered polymer ring in the bearing surfaceof the bullet may be had.

Since the invention described herein may be variously practiced withoutdeparting from the spirit and scope thereof, it is not intended that itbe limited except as is required by the appended claims.

way of the muzzle. degree of freedom What is claimed is:

1. An elongated bullet of low melting point metal selected from thegroup consisting of lead and lead alloys, said bullet being adapted tobe fired from a rifled gun and having that portion of its surface whichnormally contacts and is engraved by the rifling of the gun on firingformed in part by the periphery of an inset ring of essentially sinteredpolytetrafiuoroethylene which is conterminous with said surface andintegral with the metal of said bullet.

2. An elongated lead bullet adapted to be fired from a rifled gun inwhich that portion of its surface which normally contacts and isengraved by the rifling of the gun on firing is in part the periphery ofan inset ring of essentially sintered polytetrafiuoroethylene which isconterminous with said surface and integral with the lead of saidbullet.

References Cited in the tile of this patent UNITED STATES PATENTS

1. AN ELONGATED BULLET OF LOW MELTING POINT METAL SELECTED FROM THEGROUP CONSISING OF LEAD AND LEAD ALLOYS, SAID BULLET BEING ADAPTED TO BEFIRED FROM A RIFLED GUN AND HAVING THAT PORTION OF ITS SURFACE WHICHNORMALLY CONTACTS AND IS ENGRAVED BY THE RIFFING OF THE GUN ON FIRINGFORMED IN PART BY THE PERIPHERY OF AN INSET RING OF ESSENTIALLY SINTEREDPOLYTETRAFLIOROETHYLENE WHICH IS CONTERMINOUS WITH SAID SURFACE ANDINTERGRAL WITH THE METAL OF SAID BULLET.